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Volume 377 - 18th International Conference on B-Physics at Frontier Machines (Beauty2019) - Semileptonic decays
$R(D)$ and $R(D^*)$ at Belle
K. Hara
Full text: Not available
A new measurement of the ratio of the branching fractions
$R(D^{(*)}) = \mathcal{B}(\overline{B}\to D^{(*)}\tau^-\overline{\nu}_\tau) / \mathcal{B}(\overline{B}\to D^{(*)}\ell^-\overline{\nu}_\ell)$, $\ell = e, \mu$
is performed using a semileptonic tagging method with the data sample of $772
\times 10^6$ $B\overline{B}$ pairs collected at the Belle experiment.
The obtained results are
$R(D) = 0.307 \pm 0.037 \mathrm{(stat.)} \pm 0.016 \mathrm{(syst.)}$
$R(D^*) = 0.283 \pm 0.018 \mathrm{(stat.)} \pm 0.014 \mathrm{(syst.)}$.
These results are consistent with the SM prediction within $0.2\sigma$ and $1.1\sigma$,
Belle also performs the polarization measurements in $\overline{B}\to D^{*}\tau^-\overline{\nu}_\tau$ decays.
The first preliminary result of the fraction of the
longitudinal polarization of $D^{*-}$, $F_L^{D^*}$, is obtained to be $F_L^{D^*} =
0.60 \pm 0.08 \mathrm{(stat.)} \pm 0.04 \mathrm{(syst.)}$ with an inclusive tagging method.
The $\tau$ polarization measurement which has been performed with the hadronic tagging method is also shown.
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